Metallic Powder Mixtures

ABSTRACT

The invention relates to blends of metal, alloy or composite powders having a maximum mean particle diameter D50 of 75, preferably a maximum of 25 μm, which are produced according to a process in which a base powder is first transformed into flake-like particles and these are then crushed in the presence of milling auxiliary agents, with further additives and also the use of these powder blends and moulded objects produced from them.

The invention relates to blends of metal, alloy or composite powdershaving a mean particle diameter D50 of no more than 75, preferably of nomore than 25 μm, produced according to a process in which a base powderis first transformed into flake-like particles and these are thencrushed with further additives in the presence of milling auxiliaryagents and also the use of these powder blends and moulded objectsproduced from them.

From the patent application PCT/EP/2004/00736, not yet laid open forpublic inspection, powders are known that can be obtained by a processfor the production of metal, alloy and composite powders having a meanparticle diameter D50 of no more than 75, preferably of no more than 25μm, measured with a Microtrac® X 100 particle size analyser according toASTM C 1070-01, from a base powder with a larger mean particle diameter,the particles of the base powder being processed in a deformation stepinto flake-like particles having a ratio of particle diameter toparticle thickness of 10:1 to 10000:1 and these flake-like particlesbeing subjected in a further process step to pulverisation or to ahigh-energy load in the presence of a milling auxiliary agent. Thisprocess is advantageously followed by a de-agglomeration step. Thisde-agglomeration step, in which the powder agglomerates are broken downinto their primary particles, can be carried out for example in a gascounter-current mill, an ultrasound bath, a kneader or a rotor-stator.In this specification such powders are called PZD powders.

These PZD powders have various advantages over conventional metal, alloyand/or composite powders used for powder metallurgy applications, suchas improved green strength, compressibility, sintering behaviour, awider sintering temperature range and/or a lower sintering temperature,but also better strength, oxidation and corrosion behaviour of themoulded parts produced and lower production costs. A disadvantage ofthese powders is, for example, poorer flowability. The changedcontraction characteristics combined with the lower tap density maycause problems during powder-metallurgic processing as a result ofgreater sintering contraction. These characteristics of the powders aredisclosed in PCT/EP/2004/00736, to which reference is made.

Conventional powders, obtained for example by atomisation of metalmelts, also have disadvantages. For certain alloy compositions, known ashigh-alloy materials, in particular, these are lack of sinteringactivity, poor compressibility and high production costs. Thesedisadvantages are less significant in particular for metal injectionmoulding (MIM), slip casting, wet-spraying and thermal spray coating. Asa result of the poorer green strength of conventional metal powders (inthe sense of metal, alloy and composite powders, abbreviated to MLV)these materials are unsuitable for conventional powder-metallurgiccompression, for powder rolling and for cold isostatic pressing (CIP)with subsequent green processing, as the green compacts do not havesufficient strength for this.

The object of the present invention is to provide metal powders forpowder metallurgy, which do not have the above-mentioned disadvantagesof conventional metal powders (MLV) and the PZD powders, but combine tothe greatest possible extent their respective advantages, such as highsintering activity, good pressability, high green strength, goodpourability.

A further object of the present invention is to provide powderscontaining functional additives, which can provide the moulded objectsproduced from PZD powders with characteristic properties, such as forexample additives that increase the impact strength or abrasionresistance, such as superhard powders, or additives that facilitate theworking of the green compacts, or additives that function as templatesto control the pore structure.

A further object of the present invention is to provide high-alloypowders for the whole spectrum of powder-metallurgic moulding processes,so that applications in fields that are not accessible to conventionalmetal, alloy or composite powders, are also possible.

This object is achieved by metallic powder blends containing a ComponentI, a metal, alloy and composite powder having a mean particle diameterD50 of no more than 75, preferably of no more than 25 μm, or 25 μm to 75μm, measured with a Microtrac® X100 particle size analyser in accordancewith ASTM C 1070-01, which can be obtained by a process in which theparticles of a base powder with a larger or smaller mean particlediameter are processed in a deformation step to flake-like particleshaving a ratio of particle diameter to particle thickness of 10:1 to10000:1 and these flake-like particles are subjected in a furtherprocess step to pulverisation in the presence of a milling auxiliaryagent, a Component II, which is a conventional metal powder (MLV) forpowder metallurgy applications, and/or a Component III, which is afunctional additive. The steps of flake production and pulverisation canbe combined directly, by carrying out one immediately after the other inthe same unit under conditions adapted to the particular objective(flake formation, crushing).

This objective is also achieved by metallic powder blends containing aComponent I, a metal, alloy and composite powder, the contraction ofwhich, measured with a dilatometer according to DIN 51045-1, up to thetemperature of the first contraction maximum, is at least 1.05 times thecontraction of a metal, alloy or composite powder of the same chemicalcomposition and the same mean particle diameter D50, produced byatomisation, the powder to be investigated being compacted to a presseddensity of 50% of theoretical density before contraction is measured, aComponent II, which is a conventional metal powder (MLV) for powdermetallurgy applications and/or a Component III, which is a functionaladditive. Where a compact that can be handled cannot be produced fromconventional powders of the desired density (50%), greater densities arealso permissible, for example, by using pressing auxiliary agents.However this should be understood to mean the same ‘metallic density’ ofthe powder pressed bodies and not the average density of the MLV powderand pressing auxiliary agent.

The use of Component 1 also makes it possible to produce metallic powderblends in which the contents of oxygen, nitrogen, carbon, boron, siliconcan be precisely set. If oxygen or nitrogen enter the process, the highenergy input can lead to the formation of oxide and/or nitride phasesduring the production of Component I. Such phases may be desirable forcertain applications, as they may have a significantmaterial-strengthening effect. This effect is known as the OxideDispersion Strengthening Effect (ODS). However, the incorporation ofsuch phases is often associated with a deterioration in processingproperties (for example compressibility, sintering activity). As aresult of the generally inert properties of the dispersoids towards thealloy component, the latter may thus inhibit sintering.

Pulverising immediately distributes the phases referred to finely in thepowder produced. The phases formed (e.g. oxides, nitrides, carbides,borides) are therefore distributed considerably more finely andhomogeneously in Component I than in conventionally-produced powders.This again leads to increased sintering activity in comparison withphases of the same type incorporated discretely. This improves thesinterability of the metallic powder blends according to the invention.Such powders with finely-dispersed intercalations can be obtained inparticular by precise introduction of oxygen during the milling processand lead to the formation of very finely-distributed oxides. Specificuse of milling auxiliary agents, which are suitable as ODS particles andundergo mechanical homogenisation and dispersal during the millingprocess, is also possible.

The metallic powder blend according to the present invention is suitablefor use in all powder-metallurgic moulding processes. Powder-metallurgicmoulding processes according to the invention are pressing, sintering,slip casting, sheet moulding, wet-spraying, powder rolling (either cold,hot or warm rolling), hot pressing and hot isostatic pressing (HIP),sinter-HIP, powder charge sintering, cold isostatic pressing (CIP), inparticular with green processing, thermal spraying and deposit welding.

The use of the metallic powder blends in powder-metallurgic mouldingprocesses leads to significant difference in the processing, thephysical and material properties and allows the production of mouldedobjects, which have improved properties, although the chemicalcomposition is comparable or identical to that of conventional metalpowders. The presence of Component II allows precise ‘tuning’ ofcomponent properties such as high-temperature strength, strength,toughness, wear-resistance, oxidation resistance or porosity.

Pure, thermal spray powders can also be used as a repair solution forcomponents. The use of pure agglomerated/sintered powders according tothe patent application PCT/EP/2004/00736, not yet laid open forinspection, as a thermal spray powder allows the characteristic coatingof components with a surface layer that has better abrasion andcorrosion behaviour than the base material. These properties result fromvery finely-distributed ceramic intercalations (oxides of elementshaving an affinity with oxygen) in the alloy matrix resulting frommechanical loading during production of the powders according toPCT/EP/2004/00736.

Component I is a metal, alloy, and composite powder, which can beobtained by a two-stage process, in which a base powder is firsttransformed into flake-like particles and these are then crushed in thepresence of milling auxiliary agents. In particular, Component I is ametal, alloy and composite powder having a mean particle diameter D50 ofno more than 75, preferably of no more than 25 μm, measured with theMicrotrac® X100 particle size analyser according to ASTM C 1070-01,which can be obtained by a process in which, are obtainable from a basepowder with a larger mean particle size, the particles of the basepowder being processed in a deformation step to flake-like particleshaving a ratio of particle diameter to particle thickness of 10:1 to10000:1 and these flake-like particles being subjected in a furtherprocess stage to pulverisation in the presence of a milling auxiliaryagent.

The particle size analyser Microtrac® X100 is commercially availablefrom Honeywell, USA.

To measure the ratio of particle diameter to particle thickness, theparticle diameter and the particle thickness are measured by photo-opticmicroscopy. For this purpose, the flake-like powder particles are firstmixed with a viscous, transparent epoxy resin in a ratio of 2 parts byvolume of resin to 1 part by volume of flakes. The air bubblesincorporated when mixing are then removed by evacuation of the mixture.The now bubble-free mixture is then poured onto a level substrate androlled out into a wide sheet with a roller. In this way, the flake-Likeparticles align themselves preferably in the field of flow between theroller and the substrate. The preferred layer is characterised in thatthe normal line to the surface of the flakes is on average alignedparallel to the normal line to the surface of the level substrate, inother words, the flakes are on average arranged flat on the substrate inlayers. After hardening, samples of suitable dimensions are worked outof the epoxy resin sheet lying on the substrate. These samples arestudied with a microscope vertically and parallel to the substrate.Using a microscope with a calibrated lens and taking account of adequateparticle orientation, at least 50 particles are measured and a meanvalue is produced from the measured values. This mean value representsthe particle diameter of the flake-like particles. The particlethicknesses are measured on a vertical section through the substrate andthe sample to be analysed using the microscope with a calibrated lens,which was also used to measure the particle diameter. Care should betaken to ensure that only particles lying as nearly parallel as possibleto the substrate are measured. As the particles are coated on all sidesin the transparent resin, it is not difficult to selectsuitably-orientated particles and to assign reliably the limits of theparticles to be evaluated. Once again, at least 50 particles aremeasured and a mean value is produced from the measured values. Thismean value represents the particle thickness of the flake-like particle.The ratio of particle diameter to particle thickness can be calculatedfrom the dimensions measured before.

Fine, ductile metal, alloy or composite powders in particular can beproduced by this process. Ductile metal, alloy or composite powders areunderstood to mean those powders that, when mechanically loaded tobreaking point, undergo plastic elongation or deformation beforesignificant material damage (embrittlement of the material, breakage ofthe material) occurs. Such plastic material changes are dependent on thematerial and can range from 0.1 percent to several hundred percent, inrelation to the initial length.

The degree of ductility, i.e. the ability of materials to achieveplastic i.e. lasting deformation under the influence of mechanicalstrain, can be measured or described by means of mechanical tensileand/or pressure tests.

To measure the degree of ductility by means of a mechanical tensiletest, a so-called tensile test specimen is produced from the material tobe evaluated. The specimen can be e.g. a cylindrical specimen thediameter of which is reduced by ca 30-50% centrally along its length,over a length of ca 30-50% of the overall length of the specimen. Thetensile test specimen is loaded into the clamping device of anelectro-mechanical or electro-hydraulic tensile test machine. Beforeactual mechanical testing, length measurement sensors are placed in themiddle of the specimen over a measuring length amounting to ca 10% ofthe overall length of the specimen. These measuring sensors make itpossible to track the increase in length over the selected measurementlength whilst applying a mechanical tensile strain. The strain isincreased until the specimen breaks, and the plastic portion of thelength change is evaluated with the aid of the stress-strain chart.Materials, which in such an arrangement achieve a plastic length changeof at least 0.1%, are described as ductile according to thisspecification.

Similarly, it is also possible to subject a cylindrical materialspecimen, which has a ratio of diameter to thickness of ca. 3:1, to amechanical pressure load in a commercially available pressure testingmachine. After exerting sufficient mechanical compressive strain, thecylindrical specimen also undergoes permanent deformation. Once thepressure has been released and the specimen removed, it can be seen thatthe ratio of diameter to thickness has increased. Materials, whichachieve a plastic change of at least 0.1% in such a test are alsodescribed as ductile according to this specification.

Fine, ductile alloy powders having a degree of ductility of at least 5%are preferably produced according to the process.

The crushability of alloy or metal powders which, per se, cannot befurther crushed, is improved by the use of mechanically,mechano-chemically and/or chemically active milling auxiliary agents,which are added precisely or are produced in the milling process. Afundamental aspect of this approach is that the chemical ‘targetcomposition’ of the powder thus produced should not be changed overall,or even should be influenced in such a way that the processingproperties, such as e.g. sintering behaviour or flowability areimproved.

The process is suitable for the production of a wide variety of finemetal, alloy or composite powders having a mean particle diameter D50 ofno more than 75, preferably of no more than 25 μm.

The metal, alloy and composite powders produced are characterisedconventionally by a small mean particle diameter D50. The mean particlediameter is preferably no more than 15 μm, measured according to ASTM C1070-01 (measuring device: Microtrac® X100). For the purpose ofimproving product properties for which fine alloy powders tend to beunfavourable (porous structures, with which a certain material thicknesscan better withstand oxidation/corrosion in their sintered state), it isalso possible to set significantly higher D50 values (25 to 300 μm) thanare mostly attempted, whilst maintaining the improved processingproperties (pressing, sintering).

As a base powder, powders can be used for example, that already have thecomposition of the desired metal, alloy or composite powder. However, itis also possible to use a mixture of several base powders in theprocess, which produce the desired composition only through the choiceof a suitable mix ratio. In addition, the composition of the metal,alloy or composite powder produced can be influenced also by the choiceof milling auxiliary agent, where this remains in the product.

Powders with spherical or irregularly shaped particles and a meanparticle diameter D50, measured according to ASTM C 1070-01 normally ofgreater than 75 μm, in particular greater than 25 μm, preferably of 30to 2000 μm or of 30 to 1000 μm, or of 75 μm to 2000 μm or 75 μm to 1000μm, or 30 μm to 150 μm, are preferably used as a base powder.

The required base powders can be obtained for example by atomisation ofmetal melts and, if necessary, subsequent classification or sieving.

The base powder is first subjected to a deformation step. Thedeformation step can be carried out in known devices, for example in arolling mill, a Hametag mill, a high-energy mill or an attritor oragitated ball mill. By selecting suitable process parameters, inparticular by the effect of mechanical strains that are sufficient toachieve plastic deformation of the material or the powder particle, theindividual particles are transformed, so that they finally take the formof flakes, the thickness of which is preferably 1 to 20 μm. This cantake place for example by loading once in a roller or hammer mill, byloading several times in ‘small’ deformation steps, for example byimpact milling in a Hametag Mill or a SimoIoyer®, or by a combination ofimpact and abrasive milling, for example in an attritor or a ball mill.The high material loading during this transformation produces structuralchanges and/or material embrittlement, which can be utilised in thefollowing step to crush the material.

Known melt-metallurgy rapid-setting processes can also be used toproduce ribbons or flakes. Like the mechanically-produced flakes, theseare then suitable for the crushing process as described below.

The device in which the deformation step is carried out, the millingmedia and the other milling conditions are preferably selected in such away that the impurities resulting from abrasion and/or reactions withoxygen or nitrogen are kept at the lowest possible level and lie belowthe level critical for the application of the product, or within thespecification applying to the material.

This can be achieved, for example, by a suitable choice of material forthe milling vessel and milling medium, and/or the use of oxidation andnitridation-inhibiting gases and/or the addition of protective solventsduring the deformation step.

In a particular embodiment of the process, the flake-like particles areproduced directly from the melt in a rapid-setting step, e.g. byso-called melt spinning, by cooling on or between one or more,preferably cooled, rollers so that flakes form immediately.

The flake-like particles formed in the deformation step are subjected tocrushing. This changes first the ratio of particle diameter to particlethickness, primary particles (to be obtained by de-agglomeration) beinggenerally obtained with a ratio of particle diameter to particlethickness of 1:1 to 100:1, preferably 1:1 to 10:1. Secondly, the desiredmean particle diameter of no more than 75, preferably of no more than 25μm is set without again producing particle agglomerates that aredifficult to crush.

Crushing can be carried out, for example, in a mill, such as anexcentric vibrating mill, but also in material bed roller mills,extruders or similar devices, which effect material destruction in theflakes by means of differing movement and loading speeds.

Crushing is carried out in the presence of a milling auxiliary agent.Liquid milling auxiliary agents, waxes and/or brittle powders, forexample, can be added as milling auxiliary agents. The milling auxiliaryagents may have a mechanical, chemical or mechano-chemical action.

The milling auxiliary agent can be, for example, paraffin oil, paraffinwax, metal powder, alloy powder, metal sulfides, metal salts, salts oforganic acids and/or hard material powders.

Brittle powders or phases act as mechanical milling auxiliary agents andcan be used for example in the form of alloy, element, hard material,carbide, silicide, oxide, boride, nitride or salt powders. Pre-crushedelement and/or alloy powders are used, for example, which, together withthe base powder used, which is not readily-crushable, produce thedesired compositions in the product powder.

Powders which consist of binary, ternary and/or higher compositions ofthe elements A, B, C and/or D present in the base alloy to be used, arepreferably used as brittle powders, wherein A, B, C and D have themeaning given further below.

Liquid and/or readily-deformed milling auxiliary agents, for examplewaxes, can also be used. Examples of these are hydrocarbons, such ashexane, alcohols, amines or aqueous media. These are preferablycompounds that are required for the subsequent steps of furtherprocessing and/or can easily be removed after crushing.

It is also possible to use special organic compounds, which are knownfrom pigment production, and are used there to stabilisenon-agglomerating single flakes in a liquid environment.

In a particular embodiment, milling auxiliary agents are used, whichenter into a precise chemical reaction with the base powder to promotemilling and/or to set a particular chemical composition of the product.These can be, for example, degradable chemical compounds, of which onlyone or more constituents are needed to set a desired composition, andwherein at least one component or constituent can be largely removed bya thermal process.

Examples are reducible and/or degradable compounds, such as hydrides,oxides, sulfides, salts, sugars, which are at least partially removedfrom the crushed material in a subsequent processing stage and/orpowder-metallurgic processing of the product powder, and which togetherwith the remaining residue chemically supplement the powder compositionin the desired manner.

It is also possible, rather than adding the milling auxiliary agentseparately, to produce it in-situ during crushing. This can be done, forexample by producing the milling auxiliary agent by the addition of areaction gas, which under the crushing conditions reacts with the basepowder to form a brittle phase. Hydrogen is preferred as the reactiongas.

The brittle phases produced during treatment with the reaction gas, forexample by formation of hydrides and/or oxides, can generally be removedagain by corresponding process steps once crushing is complete or duringprocessing of the fine metal, alloy or composite powder obtained.

If grinding auxiliary agents are used, which cannot be removed, orcannot fully be removed from the metal, alloy or composite powderproduced, these are preferably selected in such a way that the remainingconstituents have a desirable influence on the properties of thematerial, such as for example the improvement of the mechanicalproperties, the reduction of susceptibility to corrosion, an increase inhardness and improvement of the abrasion behaviour or friction and slipproperties. An example of this is the use of a hard material, theproportion of which is increased in a subsequent step to such an extentthat the hard material together with the alloy component can be furtherprocessed into a hard metal or a hard metal-alloy composite material.

After the deformation step and crushing, the primary particles of themetal, alloy or composite powders produced have a mean particle diameterD50, measured to ASTM C 1070-01 (Microtrac® X100) of normally 25 μm,advantageously less than 75 μm, in particular less than or equal to 25μm.

In spite of the use of milling auxiliary agents, coarser secondaryparticles (agglomerates) with particle diameters significantly greaterthan the desired maximum mean particle diameter of 25 μm, may be formedin addition to the desired formation of fine primary particles, as aresult of the known interaction between very fine particles.

For this reason, crushing is preferably followed by a de-agglomerationstep, where the product to be produced allows or requires no (coarse)agglomerate, in which the agglomerates are broken up and the primaryparticles are released. The de-agglomeration can be carried out, forexample, by applying shearing forces in the form of mechanical and/orthermal stresses and/or by removing interlayers inserted between theprimary particles earlier in the process. The particularde-agglomeration method to be used depends on the degree ofagglomeration, the intended use and the susceptibility to oxidation ofthe very fine powder and the admissible impurities in the finishedproduct.

De-agglomeration can take place, for example, by mechanical methods,such as by treatment in a gas counter-current mill, sieving,classification or treatment in an attritor, a kneader or a rotor-statordisperser. A voltage field can also be used, such as that produced inultrasound treatment, a thermal treatment, for example dissolution orconversion of a previously-incorporated interlayer between the primaryparticles by cryo- or high-temperature treatments, or a chemicaltransformation of incorporated or purposely created phases.

De-agglomeration is preferably carried out in the presence of one ormore liquids, dispersion auxiliary agents and/or binders. In this way, aslip, a paste, a kneading composition or a suspension with a solidcontent of 1 to 95 wt. % can be obtained. Solid contents of 30 to 95 wt.% can be processed directly by known powder-technology processes, suchas for example, injection moulding, sheet moulding, coating, hotcasting, and then converted to an end product in suitable drying,debinding and sintering steps.

For de-agglomeration of particularly oxygen-sensitive powders, a gascounter-current mill is preferably used, which is operated under inertgases, such as for example argon or nitrogen.

The metal, alloy or composite powders produced are characterised by anumber of particular properties in comparison with conventional powderswith the same mean particle diameter and the same chemical composition,which are produced for example by atomisation.

The metal powders of Component I for example have excellent sinteringbehaviour. At a low sintering temperature, the same sintering densitiescan mostly be achieved, as with powders produced by atomisation. At thesame sintering temperature, higher sintering densities can be achievedin relation to the metallic portion of the pressed body on the basis ofpowder compacts of the same pressed density. This increased sinteringactivity can be seen for example in the fact that the contraction of thepowder according to the invention during the sintering process is higherup to the main contraction maximum than that of conventionally-producedpowders and/or that the (standardised) temperature, at which thecontraction maximum occurs, is lower with the PZD powder, Monoaxiallypressed bodies can produce different paths of contraction parallel andvertically to the direction of pressing. In this case, the contractioncurve is determined mathematically by addition of the contractions atthe relevant temperature. Here, the contraction in the direction ofpressing contributes one third and the contraction vertically to thedirection of pressing contributes two thirds to the contraction curve.

The metal powders of Component I are metal powders whose contraction,measured by dilatormeter according to DIN 51045-1, up to the temperatureof the first contraction maximum, is at least 1.05 times that of ametal, alloy or composite powder of the same chemical composition andthe same mean particle diameter D50, produced by atomisation, the powderto be analysed being compacted to a pressed density of 50% oftheoretical density before contraction is measured.

The metal powders of Component I are characterised as a result of aparticular particle morphology with a rough particle surface, also bycomparatively better pressing behaviour and as a result of thecomparatively broad particle size distribution, by high pressed density.This manifests itself in the fact that compacts of atomised powder withotherwise identical production conditions, have a lower bending strength(so-called green strength) than compacts of PZD powders of the samechemical composition and the same mean particle size D50.

The sintering behaviour of powders of Component I can also be influencedspecifically by the choice of milling auxiliary agents. Thus one or morealloys can be used as milling auxiliary agents, which, as a result oftheir low melting point in comparison with the base alloy, form liquidphases already during heating, which improve particle rearrangement andmaterial diffusion and thus the sintering and contraction behaviour, andthus allow higher sintering densities to be achieved at the samesintering temperature or the same sintering density at lower sinteringtemperatures than the reference powder. Chemically degradable compoundscan also be used, whose degradation products, together with the basematerial, produce liquid phases or phases with a raised diffusioncoefficient, which are beneficial to compaction.

Conventional metal powders (MLV) for powder metallurgy applications arepowders with a substantially spherical particle shape, as shown forexample in FIG. 1 of PCT/IEP/2004/00736. These metal powders may beelement powders or alloy powders. These powders are known to the personskilled in the art and can be obtained commercially. Numerous chemicaland metallurgic processes are known for their production. If finepowders are to be produced, the known processes often begin by melting ametal or an alloy. The mechanical coarse and fine crushing of metals oralloys is also frequently used for the production of ‘conventionalpowders’, but produces powder particles with a non-spherical morphology.In so far as it functions in principle, this constitutes a very simpleand efficient method of powder production. (W. Schatt, K.-P. Wieters in‘Powder Metallurgy—Processing and Materials’, EPMA European PowderMetallurgy Association, 1997, 5-10). The atomisation method is alsodecisive for establishing the morphology of the particles.

Where the melt is broken up by atomisation, the powder particles formdirectly by setting from the melt droplets produced. Depending on themethod of cooling (treatment with air, inert gas, water), the processparameters used, such as nozzle geometry, gas speed, gas temperature ornozzle material, and also the material parameters of the melt, such asmelting and setting point, setting behaviour, viscosity, chemicalcomposition and reactivity with the process media, a large number ofpossibilities arise, and also restrictions on the process (W. Schatt,K.-P. Wieters in ‘Powder Metallurgy—Processing and Materials’, EPMAEuropean Powder Metallurgy Association, 1997, 10-23).

As powder production by atomisation is of particular industrial andeconomic importance, various atomisation concepts have becomeestablished. Depending on the powder properties required, such asparticle size, particle size distribution, particle morphology,impurities and properties of the melts to be atomised, such as meltingpoint or reactivity, and also the tolerable costs, certain processes areselected. Nevertheless, in an industrial and economic respect, there areoften limits to achieving powder with a certain property profile(particle size distribution, impurity contents, yield of ‘target grain’,morphology, sintering activity etc.) at reasonable cost (W. Schatt,K.-P. Wieters in ‘Powder Metallurgy Processing and Materials’, EPMAEuropean Powder Metallurgy Association, 1997, 10-23).

The production of conventional metal powders for powder-metallurgyapplications by atomisation has above all the disadvantage that largequantities of energy and atomisation gas must be used, which makes thisprocess very costly. In particular, the production of fine powder fromhigh-melting alloys with a melting point >1400° C. is uneconomical,because on the one hand the high melting point requires a high energyinput to produce the melt and on the other tHe gas consumption increasessharply as the desired particle size falls. In addition, there are oftendifficulties, if at least one alloy element has a high oxygen affinity.Cost advantages can be achieved in the production of fine alloy powdersby using specially-developed nozzles.

In addition to the production of conventional metal powders for powdermetallurgy applications by atomisation, other single-stagemelt-metallurgy processes are often also used, such as ‘melt-spiming’i.e. pouring a melt onto a cooled roller, producing a thin, generallyeasily crushable ribbon, or ‘crucible melt extraction’ i.e. immersing acooled, profiled, rapidly-spinning roller into a metal melt, extractingparticles and fibres.

A further important variant for the production of conventional metalpowders for powder metallurgy applications is the chemical route, viareduction of metal oxides or metal salts. However, alloy powders cannotbe produced in this way (W. Schatt, K.-P. Wieters in ‘PowderMetallurgy—Processing and Materials’, EPMA European Powder MetallurgyAssociation, 1997, 23-30).

Extremely fine particles, which have particle sizes of below onemicrometer, can also be produced by combining evaporation andcondensation processes of metals and alloys, and by gas phase reduction(W. Schatt, K.-P. Wieters in ‘Powder Metallurgy—Processing andMaterials’, EPMA European Powder Metallurgy Association, 1997, 39-41).However, these processes are very costly on an industrial scale.

If the melt is cooled in a larger volume/block, mechanical process stepsfor coarse, fine, and very fine crushing are required, to produce metalor alloy powders that can be processed by powder metallurgy. A summaryof mechanical powder production is given by W. Schatt, K.-P. Wieters in‘Powder Metallurgy—Processing and Materials’, EPMA European PowderMetallurgy Association, 1997, 5-47.

Mechanical crushing, particularly in mills, as the oldest method ofparticle size setting, is very advantageous from an industrial point ofview, because it can be applied at little expense to a large number ofmaterials. However, it makes particular demands on the charge materialwith regard to the size of the pieces and the brittleness of thematerial for example. In addition, crushing cannot be continued for anindefinite time. Rather, a milling equilibrium forms, which isestablished even if the milling process is started with finer powders.The conventional milling processes are modified when the physical limitsof crushability are reached for the particular milling material, andcertain phenomena, such as for example embrittlement at lowtemperatures, or the effect of milling auxiliary agents, improve themilling behaviour or crushability. The conventional metal powders forpowder metallurgy applications can be obtained by these aforementionedprocesses.

The Components I and IL, independently of each other, can be chemicallythe same or different and can be element powders, alloy powders ormixtures thereof.

The metal powders of Components I and II may have a composition ofFormula I

hA-iB-jC-kD  (I)

wherein,

-   A stands for one or more of the elements Fe, Co, Ni,-   B stands for one or more of the elements V, Nb, Ta, Cr, Mo, W, Mn,    Re, Ti, Si, Ge, Be, Au, Ag, Ru, Rh, Pd, Os, Ir Pt,-   C stands for one or more of the elements Mg, Al, Sn, Cu, Zn, and-   D stands for one or more of the elements Zr, Hf, Mg, Ca rare earth    metal (Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm,    Yb, Lu),    and h, i, j and k give the proportions by weight, wherein    h, i, j and k, independently of each other each mean 0 to 100 wt. %,    provided that the sum of h, i, j and k amounts to 100% wt. %.

In a further embodiment of the invention

-   A stands for one or more of the elements Fe, Co, Ni-   B stands for one or more of the elements V, Cr, Mo, W, Ti,-   C stands for one or more of the elements Mg, Al and-   D stands for one or more of the elements Zr, Hf, Y, La,

in Formula I

h stands for 50 to 80 wt. % or for 60 to 80 wt. %, i means 15 to 40 wt.% or 18 to 40 wt. %, j means 0 to 15 wt. % or 5 to 10 wt. %, k means 0to 5 wt. % or 0 to 2 wt. %.

In a further embodiment of the invention, Components I or II are elementpowders or binary alloy powders, so that a moulded object, which can beobtained from a metallic powder blend according to the invention, has acorresponding, more complex composition. For example, in this embodimentof the invention a moulded object can be obtained, through the use ofbinary alloys for Components I and II, that consists of a quaternaryalloy.

In a further embodiment of the invention, Components I and II are higheralloy powders such as binary or quaternary alloy powders, so that amoulded object, which can be obtained from a metallic powder blendaccording to the invention, has a corresponding more complexcomposition. Components I and II, independently of each other, can thusalso consist of alloys containing two, three, four or five differentmetals, so that more complex alloys are possible. For example, in thisembodiment of the invention, a moulded object can be obtained throughthe use of a binary alloy for Component I and a quaternary alloy forComponent II, that consists of an alloy containing six metals.

In a further embodiment of the invention, the compositions of ComponentsI and II of the metallic powder blend and also of a moulded objectobtained from them are each different from the other.

In a further embodiment of the invention, a moulded object, which can beobtained by subjecting a metallic powder blend according to theinvention to a powder-metallurgic moulding process, has a composition ofFormula I.

In a further embodiment of the invention, the moulded object, ComponentI and/or Component II consist substantially of an alloy selected fromthe group consisting of Fe20Cr10Al0.3Y, Fe22Cr7V0.3Y, FeCrVY,Ni57Mo17Cr16FeWMn, Ni17Mo15Cr6Fe5W1Co, Ni20Cr16Cu2.5Ti1.5Al andNi53Cr20Co18Ti2.5Al1.5Fe1.5.

In a further embodiment of the invention, Component I and/or II may evenbe a powder blend of different element powders or alloy powders. Forexample a moulded object containing six metals as alloy components canbe obtained in this case by mixing a Component I, which is a binaryalloy with a Component IIa and a Component IIb, which are each binaryalloys, and subjecting them to a powder-metallurgic moulding process.

The quantity of Component II in the metallic powder blend depends on thetype and extent of the intended effect to be achieved and on the desiredchemical composition of the moulded object obtained when the metallicpowder blend is subjected to a powder-metallurgic moulding process. IfComponents I and II are identical, the chemical composition of themoulded object is already established. However, if Components I and IIhave a different composition, the composition of the resulting mouldedobject depends on the type, composition and content of Components I andII and these must be adjusted accordingly. According to the invention,moulded objects can be produced from high-alloy metallic materials usingprocesses that were previously not suited to their production. Theperson skilled in the art is, in principle, familiar with the effectsarising, so that the optimum blends for the respective application canbe established with a small number of trials. In general, theconventional metal powder is used in proportions of Component I:Component II of a ratio of 1:100 to 100:1 or of 1:10 to 10:1 or of 1:2to 2:1 or of 1:1.

The present invention can be used for the production of high-alloymaterials. Possible procedures are described in more detail here. Theproduction of complex alloy components for the metallic powder blend canin general be described as follows, the sum of the factors a, b and cbeing made up to 100 percent by weight and the symbols ABMP-bLEM-cDOTdMHM-eFUZ being used as follows:

-   BMP (base metal powder): Fe, Ni, Co-   LEM (alloy element): Cr, Al, Ti, Mo, W, Nb, Ta, V, . . .-   DOT (dopants) SE (rare earth metals), Zr, Hf; Mg, Ca-   MHM (milling auxiliary agents) Paraffin, hydrocarbons, brittle    intermetallic phases, other brittle phases (ceramics, hard    materials)-   FUZ (functional additives) Ceramics, hydrocarbons, sulfides,

The indices d and e state the quantity of milling auxiliary agent orfunctional additive that can be obtained additionally.

In one embodiment of the invention, the alloy composition is retained.The composition of the metallic powder blend is as follows:

Component I: a₁BMP-b₁LEM-c₁IDOT-d₁MHMComponent II: a₂BMP-b₂LEM-c₂DOTComponent III: −e₃FUZ

-   -   (where e₃=0)

In this case, the alloy of which the moulded object consists, which isobtained from the metallic powder blend, is composed as follows:

(a₁+a₂)BMP−(b₁+b₂)LEM−(c₁+c₂)DOT

(without milling auxiliary agents)

In this case a₁a₂ and b₁=b₂ and c₁=c₂, which means that this is amixture of the same alloys, in which Component I is a PZD powder. The(organic) milling auxiliary agent (MHN) is not mentioned, as it iscompletely removed during processing and does not change the alloy. Theproportions of Components I and II can vary between 100% Comp. I and 0%Comp. II and 1% Comp. I and 99% Comp. II, depending on the requirementsof processing or functional properties.

In a further embodiment of the invention, the alloy composition changesaccording to the proportions of Components I and II. The metallic powderblend is composed as follows:

Component I: a₁BMP-b₁LEM-d₁MHMComponent II: a₂BMP-c₂DOTComponent III: . . . not present

In this case, the alloy of which the moulded object consists, which isobtained from the metallic powder blend, is composed as follows:

(a₁+a₂)BMP−(b₁)LEM−(c₁)DOT

(without milling auxiliary agents)

In this case a₁≠a₂ and b₁≠b₂ and c₁≠c₂, which means that there are twoalloys. Component I consists only of base metal powder (BMP) and alloyelements (LEM), Component II contains the dopant in concentrated form asa compound to be added, advantageously with particular metallurgic (e.g.low melting point) and/or mechanical (e.g. brittle, easily crushable)properties. In this way, powder technological advantages (sintering witha liquid phase) can be used, to form the desired end alloys. Here, thedopant is introduced in the form of a masterbatch, which can beadvantageous depending on the type and composition of the alloys. The(organic) milling auxiliary agent is not mentioned, as it is completelyremoved during processing and does not change the alloy. The proportionsby volume of Components I and II are selected by the person skilled inthe art according to the target composition.

In a further embodiment of the invention, the alloy composition changesaccording to the proportions of Component I, IIa and IIb. The metallicpowder blend is composed as follows:

Component I: a₁BMP-b₁LEM-d₁MHM

Component II: a₂BMP-b₂LEM-c₂DOT

Component IIb: A₃BMP

In this case, the alloy of which the moulded object consists, which isobtained from the metallic powder blend, is composed as follows:

(a₁+a₂+a₃)BMP−(b₁)LEM−(c₁)DOT

(without milling auxiliary agents)

In this case a₁≠a₂≠a₃ and b₁≠b₂ and c₁≠c₂, which means that thecomponents are two alloys and a base metal powder. Component I consistsonly of base metal powder (BMP) and alloy elements, Component IIcontains as a mixture the dopant in ‘concentrated’ form together withbase metal and/or alloy elements in order to advantageously useparticular metallurgic and mechanical properties. Component IIb containsbase metals that can be produced simply and cost-effectively, which whenadded to Component I, II and IIb form the whole alloy. In this way, inaddition to the powder technological advantages of the embodimentdisclosed immediately above, technical and economic advantages can alsobe utilised. The (organic) milling auxiliary agent is not mentioned, asit is completely removed during processing and does not change thealloy.

In a further embodiment of the invention, the alloy composition changesaccording to the proportions of Components I and II. A brittle alloy isused advantageously as a milling auxiliary agent. The metallic powderblend is composed as follows:

Component I: a₁BMP-b₁LEM-d₁MHM=(a₂BMP-c₂DOT)Component II: a₃BMPComponent III: −e₃FUZ=paraffin

In this case, the alloy, of which the moulded object consists, which isobtained from the metallic powder blend, is composed as follows:

(a₁+a₂+a₃)BMP(b₁)LEM−(c₂)DOT

(without milling auxiliary agents)

In this case a₁≠a₂≠a₃, which means that there is an alloy and a basemetal. Component I consists only of base metal powder (BMP) and alloyelements (LEM). A particularly brittle composition consisting of BMP andDOT is used as a milling auxiliary agent. Paraffin in powder form ismixed in as Component III. With Component II, in this case a base metalpowder, corrections can be made to the composition. In this way thepowder technological advantages of the alloy (a₂BMP-c₂DOT) can be used.The milling auxiliary agent is not listed separately, as it disappearsinto the alloy of which the moulded object consists.

In a further embodiment of the invention, the composition changesaccording to the proportions of Component I and II. A brittle alloya₂BMP-c₂DOT is used as the milling auxiliary agent, organic constituentsand ceramic particles are used as a functional additive (FUZ). Themetallic powder blend is composed as follows:

Component I: a₁BMP-b₁LEM-d₁MHM=(a₂BMP-c₂DOT)Component II: a₂BMPComponent III: −e₃FUZ=PVA, ceramic

In this case, the alloy of which the moulded object consists, which isobtained from the metallic powder blend, is composed as follows;

(a₁+a₂+a₃)BMP=−(b₁)LEM−(C₂)DOT

(without grinding auxiliary agents)

In this case a₁≠a₂≠a₃, which means that there is an alloy and a basemetal powder. Component I consists of base metal powder and alloyelements. A brittle composition consisting of base metal and dopant isused as the milling auxiliary agent. Corrections can be made to thecomposition with the base metal powder. Component III contains PVA(polyvinyl alcohol) and ceramic particles, which are advantageous forfarther processing, for example by spray drying. This blend can beprocessed to a thermal spray powder for example. In this way, the powdertechnological advantages of the alloy (a₂BMP-c₂DOT) and the action offunctional additives (hardness, resistance to wear) can be utilised, ifthe powder is processed accordingly, for example by thermal spraying.

The metallic powder blend can contain functional additives as ComponentIII. Functional additives can give characteristic properties to objectsmoulded from PZD powders, such as for example additives that increasethe impact strength or resistance to abrasion, such as superhardpowders, or additives that facilitate processing of the green compactsby reducing the brittleness of the green compact and/or increasing thegreen strength, or additives that act as templates to control the porestructure or surface properties.

Functional additives are understood to mean additives to be incorporatedhomogeneously, which are either largely or completely retained in thefinished product, a moulded object, or which are largely or completelyremoved from the product.

The first of these are functional additives, which control themechanical properties, such as for example hardness, strength, dampingor impact strength, or the chemical properties such asoxidation/corrosion behaviour or functional properties such astribology, haptics, electrical and magnetic conductivity, modulus ofelasticity, electrical burn off behaviour, magnetostrictive behaviour,electrostrictive behaviour by their proportions and primary properties.

The complex mechanical, chemical and Functional properties can bebrought about by the incorporation of various phases/constituents, suchas chemical particles or hard materials, for example carbides, borides,nitrides, oxides, silicides, hydrides, diamonds, in particular carbides,borides and nitrides of the elements of groups 4, 5 and 6 of theperiodic system, oxides of the elements of groups 4, 5 and 6 of theperiodic system and also oxides of aluminium and rare earth metals,silicides of aluminium, boron, cobalt, nickel, iron, molybdenum,tungsten, manganese, zirconium, hydrides of tantalum, niobium, titanium,magnesium and tungsten; slip additives with lubricant properties such asgraphite, sulfides, oxides, in particular molybdenum sulfide, zincsulfide, tin sulfides (SnS, SnS₂), copper sulfide and also intermetalliccompounds with particular magnetic or electrical properties on a rareearth-cobalt or rare earth-iron base.

By this means, the coating of superhard powders with PZD powders canalso be achieved using a metallic powder blend. This is advantageouslyachieved by fluidised bed granulation.

Coarse (50-100 μm) hard material particles of BN and TiB₂ for example,can be used as feedstock for fluidised bed granulation and can beprovided with a corrosion—resistant coating. Thus it is possible toserve new applications in the field of wear under high corrosive andmechanical loads. After coating, the agglomerates are debound, sinteredin an inert atmosphere and applied by thermal spraying.

In the second case, in other words when using functional additives thatare largely or completely removed from the product, the additives usedare so-called place-holders which are removed by suitable chemical orthermal processes and thus function as a template. These can behydrocarbons or plastics. Suitable hydrocarbons are long-chainhydrocarbons such as low-molecular waxy polyolefins, such aslow-molecular polyethylene or polypropylene, and also saturated, whollyor partially unsaturated hydrocarbons having 10 to 50 carbon atoms, orhaving 20 to 40 carbon atoms, waxes and paraffins. Suitable plastics arein particular those with a low ceiling temperature, in particular with aceiling temperature of less than 400° C., or lower than 300° C. or lowerthan 200° C. Above the ceiling temperature, plastics arethermodynamically unstable and tend to degrade into monomers(depolymerisation). Suitable plastics are, for example, polyurethanes,polyacetals, polyacrylates, in particular polymethyl methacrylate, orpolystyrene. In a further embodiment of the invention, the plastic isused in the form preferably of foamed particles, such as for examplefoamed polystyrene beads, as used as a preliminary material orintermediate in the production of packaging or thermal insulationmaterials. Inorganic compounds tending towards sublimation can also actas place-holders, such as for example some oxides of refractory metals,in particular oxides of rhenium and molybdenum, and also partially- orfully-degradable compounds such as hydrides (Ti hydride, Mg hydride, Tahydride), organic (metal stearate) or inorganic salts.

By adding these functional additives, largely dense components (90 to100% of theoretical density), low-porosity (70 to 90% of theoreticaldensity) and high-porosity (5 to 70% of theoretical density) componentscan be produced, by subjecting a metallic powder blend according to theinvention containing such a functional additive as a place-holder to apowder-metallurgic moulding process.

The quantity of functional additives depends on the type and extent ofthe intended effect to be achieved, with which the person skilled in theart is, in principle, familiar, so that the optimum blends can beestablished with a small number of trials. When using these compounds,care should be taken to ensure that the compounds used asplace-holders/templates are present in the metallic powder blends in astructure suitable for their purpose, in other words in the form ofparticles, as a granulate, powder, spherical particles or similar.

In general, the functional additives are used in proportions ofComponent I Component III in a ratio 1:100 to 100:1 or of 1:10 to 10:1or 1:2 to 2:1 or of 1:1. If the functional additives are hard materials,for example tungsten carbide, boron nitride or titanium nitride, theseare advantageously used in quantities of 3:1 to 1:100 or of 1:1 to 1:10or of 1:2 to 1:7 or of 1:3 to 1:6.3.

In a further embodiment of the invention, the functional additives areadvantageously used in quantities of 3:1 to 1:100 or of 1:1 to 1:10 orof 1:2 to 1:7 or of 1:3 to 1:6.3. In a further embodiment of theinvention the metallic powder blend is a mixture of Component I withComponent II and/or Component III, provided that the ratio of ComponentI to Component III is 3:1 to 1:100 or 1:1 to 1:10 or 1:2 to 1:7 or 1:3to 1:6.3

In a further embodiment of the invention the metallic powder blend is amixture of Component I with Component II and/or Component III, providedthat, if a hard material is present in Component III, the ratio ofComponent I to Component III is 3:1 to 1:100 or 1:1 to 1:10 or 1:2 to1:7 or 1:3 to 1:6.3.

In a further embodiment of the invention, the metallic powder blend is amixture of Component I with Component II and/or Component III, providedthat, if tungsten carbide is present in Component III, the ratio ofComponent I to Component III is 3:1 to 1:100 or 1:1 to 1:10 or 1:2 to1:7 or 1:3 to 1:6.3.

Further additives will improve in particular the processing propertiessuch as pressing behaviour, strength of the agglomerates orre-dispersibility. These can be waxes, such as polyethylene waxes oroxidised polyethylene waxes, ester waxes such as montanic acid ester,oleic acid ester, esters of linoleic acid or linolenic acid or mixturesthereof, paraffins, plastics, resins such as for example colophony,salts of long-chain organic acids, such as metal salts of montanic acid,oleic acid, linoleic acid or linolenic acid, metal stearates and metalpalmitates, for example zinc stearate, in particular of the alkali andearth alkali metals, for example magnesium stearate, sodium palmitate,calcium stearate, or slip agents. These are substances that are normalin powder processing (pressing, MIM, sheet moulding, slip casting) andare known to the person skilled in the art. The compaction of the powderto be analysed can be carried out with the addition of conventionalauxiliary agents which assist pressing, such as for example paraffinwaxes, or other waxes or salts of organic acids e.g. zinc stearate.Suitable additives are further described in W. Schatt, K.-P. Wieters,‘Powder Metallurgy—Processing and Materials’, EPMA European PowderMetallurgy Association, 1997, 49-51’, to which reference is made.

The following examples serve to explain the invention in more detail.The examples are intended to facilitate understanding of the invention,and should not be understood as a restriction thereof.

EXAMPLES

The mean particle diameters D50 given in the examples were measured witha Microtrac® X100 from Honeywell, US, according to ASTM C 1070-01.

Example 1

An argon-atomised alloy melt of the type Nimonic® 90, with thecomposition Ni20Cr16Co2.5Ti1.5Al was used as the base powder. The alloypowder obtained was sieved to between 53 to 25 μm. The density was ca8.2 g/cm³. The particles of the base powder were largely spherical.

The base powder was subjected to deforming pulverisation in a verticalagitated ball mill (Netzsch Feinmalitechnik; type: PR 1S), so that theoriginally spherical particles became flake-like. The details of theparameters used are as follows:

Pulverisation vessel volume: 51 Speed: 400 rpm Peripheral speed: 2.5 m/sBall charge: 80 vol. % (bulk volume of balls) Pulverisation vesselmaterial: 100Cr6 (DIN 1.3505: ca 1.5 wt. % Cr, ca 1 wt. % C, ca. 0.3 wt.% Si, ca 0.4 wt. % Mn, <0.3 wt. % Ni, <0.3 wt. % Cu, rest Fe) Ballmaterial: Hard metal (WC-10Co) Ball diameter: Ca 6 mm (total mass: 25kg) Powder weighed in: 500 g Duration of treatment: 2 h Solvent: Ethanol(ca 2 l).

This was followed by pulverisation. A so-called excentric vibrating mill(Siebtechnik GmbH, ESM 324) was used for this, with the followingprocess parameters:

Pulverisation vessel volume: 5 l, operated as a satellite (diameter 20cm, length ca 16 cm) Ball charge: 80 vol. % (bulk volume of balls)Pulverisation vessel material 100Cr6 (DIN 1.3505: ca 1.5 wt. % Cr, ca 1wt. % C, ca. 0.3 wt. % Si, ca 0.4 wt. % Mn, <0.3 wt. % Ni, <0.3 wt. %Cu, rest Fe) Ball material: 100 Cr6 Ball diameter: 10 mm Powder weighedin: 150 g Pulverisation auxiliary agent: 2 g paraffin Vibrationamplitude: Ca 10 mm Pulverisation atmosphere: Argon (99.998%)

After a pulverising time of 2 hours very fine particle agglomerates areobtained. In an REM image of the product obtained at a magnification of1000, the cauliflower-like structure of the agglomerate (secondaryparticles) can be seen, the primary particles having particle diametersof far less than 25 μm.

A sample of the primary particles or very fine particle agglomerates wassubjected in a third process step to de-agglomeration by a 10minute-long ultrasound treatment in isopropanol in a TG 400 ultrasoundapparatus (Sonic Ultraschallanlagenbau GmbH) at 50% of the maximumoutput in order to obtain separated primary particles.

The particle size distribution of the de-agglomerated sample wasmeasured by Microtrac® X100 (manufacturer: Honeywell/US) according toASTM C 1070-01. The D50 value of the base powder amounted to 40 μm andhad fallen to ca 15 μm as a result of the treatment.

The residual quantity of primary particles from pulverisation wassubjected in an alternative third process step to de-agglomeration bytreatment in a gas counter-current mill with subsequent ultrasoundtreatment in isopropanol in a TG 400 ultrasound apparatus (from SonicUltraschallanlagenbau GmbH) at 50% of maximum output. The particle sizewas again measured by Microtrac® X100. The D50 value was now only 8.4μm.

The paraffin pulverisation auxiliary agent incorporated can be removedduring powder-metallurgic further processing of the alloy powder bythermal degradation and/or evaporation or can serve as a pressingauxiliary agent.

A metallic powder blend according to the invention was produced asfollows from the PZD powder obtained as disclosed above:

5 kg Nimonic® 90 PZD powder (d50: 10 μm and d90; 20 μm), produced asdisclosed above and 5 kg spherical (gas-atomised) Nimonic® 90 powder(d50: 10 μm and d90: 20 μm) are added to an Eirich mixer together with233 g of a pressing auxiliary agent in powder form (Licowax C). Over aperiod of 20 minutes the three constituents are intensively mixed witheach other. This powder is called VSP-711.

Analogously to this, 10 kg purely atomised (conventional) powder(Nimonic® 90 powder (d50: 10 μm and d90: 20 μm)) is processed in thesame way, however 300 g Licowax is added. This powder is called KON-711.

Both powders are processed by monoaxial pressing at a pressure of 500MPa to cylinders 10 mm in length with a diameter of 30 min. The presseddensity of KON-711 was 75% of theoretical density, however the testspecimen had only a low green strength. The specimens obtained fromVSP-711 had significantly improved strength, in spite of their lowertheoretical density (70%).

For the exact measurement of green strength, square-shaped pressedbodies are produced at a pressing pressure of 500 MPa. FIG. 1 shows aconnection in principle between the powder grades VSP_(—)711 andKON_(—)711 with various contents of pressing auxiliary agent and thegreen strength. The green strength of the pressed bodies produced fromVSP_(—)711 is up to 2.5 MPa under the conditions described and is thusat least twice that of the reference sample KON_(—)711. The pressed bodystrength of test specimens with a right-angled cross-section underbending strain was determined in accordance with DIN ISO 3995/1985. Theresults of these measurements are listed in Table 1.

TABLE 1 Green strength Paraffin content Green strength [MPa] (pressingauxiliary agent) according to DIN ISO 3995 % KON_711 VSP_711 0.7 nmb 0.72 — 1.7 3 1.2 2.5 4 2.1 — Nmb: not measurable, specimen disintegrates onhandling

Both powders (VSP-711 and KON-711) are pressed in a metal powder pressto a further test specimen, a PM tensile test bar in accordance with DINISO 3927 with an area of 6.35 cm² (parallel to the direction ofpressing) and a length of ca 5 mm. The pressure is varied from 300 to800 NWa. The density of the components increases with the increase inpressure. Table 2 describes this dependency of the influence of thepressing pressure on the green strength of tensile test specimenspressed directly from the powders as (A (area in the direction ofpressing): 6.35 cm²; L (length of the specimen in the direction ofpressing): 4-5 mm). It should be borne in mind here that the densityvalues given relate to the mixture of metal powder and pressingauxiliary agent (3% Licowax).

TABLE 2 Pressed density Pressed density/g/cm³ Pressed density/MPaKON_7.1 VSP_7.1 300 5.8 5.65 400 5.95 5.7 500 6.1 5.8 600 6.2 5.95 7006.3 6 800 6.4 6.05

The PM tensile test bars are debound in a gas stream under hydrogen at aheating rate of 2 K/min from room temperature to 600° C. and thensintered in a high vacuum at ca 10⁻³ mbar at a temperature of 1290° C.for 2 h. The specimen of the powder type KON-711 shows damage (cracks,signs of destruction) after debinding and sintering, which was notvisible in the pressed state. In contrast to this, the tensile testspecimens of VSP-711 show no damage and also have an even specimensurface with little roughness. The specimens are shown in FIG. 2. Inaddition, partial quantities of both types of powder after debinding ata heating rate of 2 K/min from room temperature to 600° C. are compactedunder hydrogen by hot pressing (1150° C./2 h/35 MPa/nitrogen) in agraphite mould. After hot pressing, the temperature is reduced by ca 5to 15 K/min, until room temperature is reached. The discs thus formedhave a density of 8.18 g/cm³ (KON-711) and 8.14 g/cm³ (VSP-711). Thesediscs (diameter: 100 mm; thickness ca 5 mm) are reduced to a thicknessof 3.5 mm by grinding on both sides. Flat tensile test specimens areproduced from them by water jet cutting as shown in FIG. 3, themechanical properties of which are evaluated in a tensile test machine(Rm, strain at break in the tensile test; Pp0.2, mechanical strain atwhich elongation of the tensile test specimen is measured at 0.2%). Themeasurement curves of the tensile tests are given in FIG. 4, and allow acomparison of strength at room temperature.

Pressed bodies were pressed at 500 MPa and sintered in a kiln at 1300and 1330° C. for two hours in an argon-hydrogen atmosphere (6.5 vol. %H₂), after which the organic pressing auxiliary agent has been removedup to 600° C. under hydrogen. The results are presented in Table 2b.

TABLE 2b Sintering conditions and sintering densities 3% PHM 3% PHMChanges in density at 1300° C./2 h/ 1330° C./2 h/ temperature increaseof Specimen ArH₂ ArH₂ 30° C. name [g/cm³] [TD] [TD] KON_7.1 7.35 (90%)7.72 (94%) 4% VSP_7.1 7.5 (91%) 7.84 (96%) 5%

A further peculiarity lies in the pore structure of the specimensproduced from KON-711 and VSP-711, which is shown in FIG. 5.

Example 2

Production of a readily-compressible, flowable and readily-sinterablegranulate in the following manner:

5 kg Nimonic® 90—PZD powder (d50: 10 μm and d90: 20 μm), produced as inExample 1, and 5 kg spherical (gas-atomised) Nimonic® 90 powder (d50: 10μm and d90: 20 μm) are added to 2-3 l water together with an organicbinder (polyvinyl alcohol, PVA, 3 wt. %) and a surface-activestabiliser. This mixture is dispersed until a stable suspension hasformed. This suspension is processed by spray-drying to an agglomerateof largely spherical single particles having a diameter of 1 to 150 μm.Heated nitrogen (gas temperature 30 to 80° C.) in counter-current isused as the working gas to dry the suspension. The gas mixture formedduring drying is released into the environment through a filter at thespray dryer outlet.

To improve further processability and to ensure compliance with healthcriteria, the ‘powdery’ fine content (<10 μm) and the content ofgrains >150 μm, which are too coarse are separated off by sieving. Sucha granulate (−150 μm+10 μm) possesses excellent flow behaviour. Thegranulate thus obtained is called VSP-712.

In parallel with the production of this granulate, an atomised(conventional) powder (10 kg) (Nimonic® 90—powder (d50: 10 μm and d90:20 μm)) is processed in the same way to a granulate (−150 μm+10 μm).This powder is called KON-712.

Both powders (VSP-712 and KON-712) are evaluated in the same way—asdescribed in Example 1—for the pressing properties, green compactstrength, sintering behaviour and surface quality (roughness) of thesintered parts. The result corresponds with the data determined in theexample given above.

Example 3 Production of a Densely-Pouring Granulate

In each case, a pressed body was produced by cold isostatic pressing(CIP) using the powder blends VSP-711 and KON-711 produced in Example 1.For this purpose, the granulate is poured into a rubber mould, sealedwith a gas-tight seal and then compacted at a hydrostatic pressingpressure of 2000 bar. A compaction of 70% TD is measured on the pressedbodies of KON-711, however VSP-711 achieves a pressed density of ca 65%TD. The CIP pressed bodies were then broken down one after the other bymachining (loaded into a lathe and cut into coarse ‘chips’). In the caseof VSP-711 a large proportion (>50% with a particle size of d50; >100μm) can successfully be processed into coarse grains. A primarilypowdery product (particles >100 μm (<5%)) is obtained from the pressedbodies of KON-711.

These pre-granulates are then processed further with a sieve granulatorplate. This process rounds off the edges of the ‘powder chips’,producing a more flowable granulate. After sieving, a fraction −65 μm+25μm, that is a fraction with a particle size of less than 65 μm andgreater than 25 μm, is obtained. This granulate can be further processedby powder-metallurgic moulding processes. The fractions are calledVSP-721 and KON-721. The total yields from the production of ahigh-density and flowable granulate are 20 to 50% in the case of VSP-721and <20% in the case of KON-721. The granulate portions not lying withinthe desired grain band can be recycled in the production process for theCIP bodies.

The investigation of the processing properties of the metallic powderblends VSP-721 and KON-721 from Example 2 (green strength, sinteringproperties) produces comparable results. VSP-721 has a higher greenstrength and higher sintering density in comparison with KON-721 at apre-determined sintering temperature, when using the same initialdensities.

Example 4 Production of a Porous Body of VSP-721, KON-721 and AtomisedPowder VER-6525 (Fraction: −65+25 μm) of the Same Composition

The VSP-721 and KON-721 granulates produced previously and a powder,VER-6525, of the same composition and same particle size as thegranulate used (−65/+25) produced by protective gas atomisation, areprocessed in the following way to produce porous moulded bodies:

Each of the three grain types is first placed in each of three identicalsintering pans (base area: 6 cm×2 cm; pouring height: 3 cm). These areheated under hydrogen in a kiln at a rate of 2 K/min to a temperature of600° C. for debinding. This is followed by heating to 1250° C. at aheating rate of 10 K/min. The temperature of 1250° C. is maintained for2 h, and the kiln containing the sintered bodies is then brought to roomtemperature at a rate of 10 K/min.

The (contracted) moulded bodies formed are removed and evaluated in thethree-point bending test. This shows that the moulded bodies achieve thefollowing, very different, bending strengths: VSP-721: 40-ca 20 MPa,KON-721: ca. 20-5 MPa and VER-6525: <5 MPa. The comparatively highsintering activity of the variant VSP-721 therefore allows production ofsufficiently strong moulded bodies, as required for example for use infilter elements. Optimisation of the sintering conditions allows thestrength of VSP-721 to be increased to over 50 MPa.

Example 5 Porous Tube

Production of a porous body in the form of a tube, by sintering a powdercharge of high-density granulates (VSP-721, KON-721) and a powderproduced by atomisation (VER-6525) of the same chemical composition andparticle size as the granulate. A correspondingly produced granulate andthe roughly-atomised powder are each put into a ceramic mould with acore that allows full burn out. The core is in the form of a thin-wallplastic tube, which is sufficiently stable to withstand the pressure ofthe powder over its area after filling. It is filled only with a narrowgranulate or powder fraction (−65+25 μm) produced by sieving.

In a subsequent step, the organic constituents and the inserted tube areremoved by thermal decomposition or expulsion in a kiln and at the sametime, pre-sintering is started at a higher temperature (1000° C.). Thepre-sintered bodies are then placed, still vertically, into anotherkiln, which reaches a temperature of 1300° C. at high gas purity(vacuum, pressure of 10⁻² mbar). After sintering, a moulded body of theVSP-721 granulate is obtained, which has sufficient contraction and alsosufficient strength. The moulded body of KON-721, on the other hand, hasless strength. The moulded body of the coarse powder (VER_(—)6525)achieved only a strength of ca 5 MPa under the conditions used,rendering industrial use impossible because of insufficient strength.

Example 6 Powder-Moulded Bodies of High-Strength Granulates

The granulates VSP-721 and KON-721 disclosed above are poured into thecavity of a powder pressing mould of a monoaxial press. Moulded bodiesare produced under monoaxial pressing pressure of 700 MPa, which havethe following densities: VSP-721: 5.3 g/cm³ (65% of theoretical density)and KON-721 ca 6 g/cm³ (73% of theoretical density). The green strengthsare 10 to 15 MPa for moulded bodies of VSP-721 and 2 to 5 MPa formoulded bodies of KON-721. After sintering according to thetemperature-time programme disclosed in Example 4, the moulded bodies ofVSP-721 achieve densities of 7.8 g/cm³ (95% of theoretical density), themoulded bodies sintered from KON-721 achieve densities of 7.7 g/cm³ (94%of theoretical density). A typical structure is shown in FIG. 5.

Example 7

Fluidised bed granulation for the production of good flow- andpress-ready powders The processing of PZD powders (NIMONIC® 90 accordingto Example 1) by fluidised bed granulation (using the ProCell machine,from Glatt) allows the production of agglomerates with particlediameters of 10 to ca 300 μm. An aqueous suspension is produced, whichis sprayed into a fluidised bed chamber. When the material jetted in isdried, tiny agglomerates are first formed, which are built up fromseveral primary particles. These act as seeds for fluidised bedgranulation. Further separation and drying of droplets producesagglomerates of growing diameter. This growth process is accompanied byimpacts between the growing particles, achieving compaction of thesurface. As a result of the binder contained in the suspension theprimary particles adhere to the surface of the seeds and growingagglomerates. The particle size and agglomeration properties can beinfluenced by appropriate setting of flow conditions and air quantities.Agglomerates produced in this way have particularly good homogeneity ofthe components in the single-cell agglomerate grain.

Example 8 Production of Coarse Powder by Agglomeration in a Mill

By using pure Nimonic® 90 PZD powder with a d50 of 10 μm and d90 of 20μm produced in the same way as Example 1, it is possible to carry out anagglomeration, in which the primary properties of the very fine powder(in particular sintering and pressing behaviour) are largely retained.

In detail, 600 g of the PZD powder is added to the measuring containerof an excentric vibrating mill. Steel balls of the material 100Cr6 (DIN1.3505) with a diameter of 15 mm are used. After a milling time of 1 hat a speed of 1500 rpm in argon 4.8 as the medium, a ball fill level of80% and a milling vessel volume of 51, a clearly ‘coarsened’ powder isremoved from the mill. The particle size d50 is ca 40 μm.

Example 9 Metallic Powder Blend with Functional Components by SprayDrying

Production of a readily-flowable granulate for use as a powder forthermal spraying in the following way:

A spherically atomised Ni17Mo15Cr6Fe5W1Co alloy with a mean particlediameter D50 of 40 μm, which is commercially available under the brandname Hastelloy® C, was subjected to a deformation step as disclosed inExample 1.

The pulverisation of the flake-like particles formed was carried out inan excentric vibrating mill in the presence of tungsten carbide as apulverisation auxiliary agent under the following conditions:

Pulverising vessel volume: 51 Ball charge: 80 vol. % Pulverising vesselmaterial: 100Cr6 (DIN 1.3505) Ball material: Wc-10Co hard metal materialBall diameter: 6.3 mm Powder weighed in: 150 g Vibration amplitude: 12mm Pulverising atmosphere: Argon (99.998%) Duration of treatment: 90minutes Pulverising auxiliary agent: 13.5 g WC (D50 = 1.8 μm)

Pulverisation produced an alloy-hard material composite powder, thealloy component of which was crushed to a mean particle diameter D50 ofca 5 μm and the hard material component to a mean particle diameter D50of ca 1 μm. The hard material particles were distributed largelyhomogeneously in the volume of the alloy powder.

1.5 kg of the Hastelloy C® PZD powder thus obtained having a d50 of 5 μmand d90 of 10 μm and 9.5 kg tungsten carbide (d50: 1 μm, d90: 2 μm) areprocessed together by spray granulation, as described in Example 2 forthe production of VSP-712, to form a granulate. The parameters for spraygranulation were set in such a way as to produce a minimum proportion offine particles. In order to remove the portions that were unsuitable forfurther processing (thermal spraying), the particles with a diametergreater than 65 μm were sieved out and the coarse portion was fed backinto the spray-ready suspension (mixed in). The fraction with a diameterof less than 65 μm is debound in a sintering boat with a base area of 15cm×15 cm filled to a level of 3 cm and then debound under hydrogen(heating at a heating rate of 2 K/min to 600° C.) and sintered at atemperature of 1150° C. The sinter cake is removed after cooling andprocessed further by lightly crushing in a mortar. The fine portion thusformed is classified with a 50 μm sieve for the ‘top’ and with a 25 μmsieve for the ‘bottom’. The fraction thus formed with a particle size ofless than 50 μm and greater than 25 μm is applied by thermal spraying(high-speed flame spraying) as a wear and corrosion-resistant layer to aHastelloy C material with low wear-resistance. The part image ‘B’ inFIG. 6 contains the result of this coating. It can be observed that ahomogeneous matrix alloy is formed, which encloses the hard materialparticles, and thus allows the expected corrosion and wear resistance.In contrast to this, the use of elementary base powders (part image‘A’), which are granulated in s similar way to produce spray-readypowders, results in inhomogeneities in the layer produced. Under theconditions of a corrosive environment, this can lead to increasedcorrosion.

Example 10 Production of a Readily-Re-Dispersible Spray Granulate [LRDG]

The granulate is produced following the method in Example 2. However, amixture of benzene (ca 10 vol. %) and ethyl alcohol (ca 90 vol. %) isused as the solvent and polymethyl methacrylate (PMMA) is used as theplastic. Spray drying, taking account of the conditions for handlinghighly flammable solvents, produces a granulate in which the individualparticles (Hastelloy C and tungsten carbide) form a largely strong bond.The parameters for spray granulation are set in such a way, that coarsegranulate with a low content of fine particles is formed, which has goodflowability (d50: 100 μm, d90: 150 μm). By investigating individualnarrower fractions by x-ray fluorescence analysis it can be demonstratedquantitatively that the same chemical composition and therefore the sameratio of powder constituents used is present in the different fractions.On this basis, it can be concluded that the granulate produced ishomogeneously distributed, and also because separation is unlikely froma chemical point of view, even if individual constituents of thefraction separate. Even after a longer period of movement—for examplewhen determining the capped density to DIN EN ISO 787-11 or ASTM B 527,only marginal changes in the particle size distribution arise, fromwhich it can be concluded that a strong bond between the powderconstituents used has been achieved in the granulate.

Example 11 Production of a Powder-Containing Feedstock of ReadilyRe-Dispersible Granulates (LRDG) for Further Processing by Metal PowderInjection Moulding

By stirring the granulate produced in Example 10 into alcohol, theindividual particles (Hastelloy C and tungsten carbide) can be released.The addition of waxes, polypropylene and stabilisers and thesimultaneous exertion of high shear forces on a shear roller at asufficiently high processing temperature, achieves a homogeneousdistribution of the powdery functional materials in the organicenvironment. The bubble-free composition is processed via a granulationsystem into a readily conveyable and homogeneously melting coldgranulate. This can then be added to the dispenser system of a metalpowder injection moulding machine, heated, and injection moulded underprocess parameters to be determined (temperature, pressure, pressurechange, after pressure, cooling time in the injection mould etc). 80 to95% of the organic constituents are extracted from theseinjection-moulded parts by solvent extraction. This is followed bythermal residual debinding by slow heating of the test specimens underhydrogen (heating rate of 1 K/min from room temperature to 600° C.). Theparts are pre-sintered at a temperature of 1000° C. under hydrogen inthe same kiln. The sintering of these specimens is then completed in avacuum kiln at a pressure of ca 10⁻² to 10⁻³ mbar (heating at 5 K/minfrom room temperature to 1250° C., 2 h holding time at 1250° C. andcooling at 10 K/min to room temperature).

Example 12 Production of a Constituent by Cold Powder Rolling

The granulates VSP-712 and KON-712 produced in Example 2 are placed oneafter the other into the nip of a vertical powder rolling machine andcompressed. In the case of VSP-712, this pressing produces in aneasy-to-handle sheet with a green strength of 2 to 10 MPa. With thegranulate KON-712, it is not possible to remove test specimens on whichthe green strength can reliably be measured.

By thermal post-treating, debinding and sintering as described underExample 11, a sheet of VSP-712 can be produced which, depending on thesintering temperature selected, can be dense (93 to 98% of theoreticaldensity) or porous (60 to ca 90% of theoretical density). In spite ofthe low density of the porous structure, these sheets still have a highstrength of at least 50-100 MPa.

Example 13 Component Produced by Powder Rolling-Sheet Production

The granulates VSP-712 and KON-712 produced in Example 2 are debound asa loose powder charge and pre-sintered to stabilise (compact) thegranulate. This takes place under the conditions described in Example 5for debinding/pre-sintering to 1000° C. After de-fragmentation,including classification to −50+25 μm as described in Example 9, thegranulate thus formed is processed in each case by powder rolling into agreen ribbon. The strength of the green ribbon is sufficient in the caseof the granulate VSP-712 for further processing by sintering. Thefragments of KON-712 are unsuitable for the intended further processinginto a sheet. If the VSP-712 green ribbon is sintered at a temperatureof 1300° C., as described in Example 5, a density of over 92% oftheoretical density can be achieved.

Example 14 Component Produced by Hot Post-Compacting by Rolling

The green ribbon described in Example 13 must not necessarily becompacted by sintering. A simple option for compaction is to heat thegreen ribbon inductively under an inert protective gas atmosphere(argon) to 1100° C., before running it into a roll nip and to subject itto intensive pressure loading at this temperature. This will very simplyproduce a sheet-like component in which complete compaction (>98% oftheoretical density) or a desired residual porosity (50 to 90% oftheoretical density) can be set by varying the roll nip. Here too, thevariant KON-712 has lower green strength to obtain a sintered component.

Example 15 Component Produced by Sheet Moulding, Debinding and Sintering

On the basis of and following the method described in Example 10 forproducing a readily re-dispersible powder blend, a granulate isproduced, which consists only of Hastelloy C powder. The tungstencarbide portion is omitted to allow a sheet to be produced that consistsonly of an alloy.

In the same way as and following the process described in Example 11, asheet-mouldable, pore-free composition is produced by intensivepulverisation.

This composition is continuously applied to a smooth surface by bladecoating. Drying produces as a green body a metal-powder-filled sheetwith organic constituents, which is rubber-like in nature. This greenbody is now subjected to debinding by heating from room temperature to600° C. at a heating speed of 0.1 K/min. The part is then subjected tosintering under the conditions described in Example 5, to achieve anincrease in strength. Linear contraction typically occurs in this step.This can amount to 10- to 25%, depending on the sintering temperatureand time.

Example 16 Component with ‘Normally’ Set Porosity

A green compact produced as in Example 15 is treated in a stamping toolin the shape of a needle press (stamp formed from needles with adiameter of 0.1 to 0.5 mm) in such a way that tube-like deformationsremain vertically to the normal line to the surface.

After debinding and sintering under the conditions described in Example5, a sheet is formed, which consists of dense material areas and porechannels lying on a normal line to the surface. The flow resistance caneasily be set by the number and diameter of the channels, without theparticle size of the powder particles directly playing a role, which canbe important for the setting of any corrosion and oxidation properties,if very fine powder particles are used.

Example 17 Blend of VSP and Organic Place-Holders for the Production ofFine-Cell Porous Structures

A bubble-free feedstock of ‘honey-like’ viscosity is produced in akneader from 3.7 kg PZD powder (VSP-711), 148 g powdery (<30 . . . 50μm) polymethyl methacrylate (PMMA) and a sufficient quantity of amixture of benzene (ca 10 vol. %) and ethyl alcohol (ca 90 vol. %).0.671 foamed polystyrene beads (Ø 1 to 1.5 mm) are added to thisfeedstock in the kneader. This composition (volume ca 0.9 . . . 1.1 l)is placed into a flat ceramic mould (ca 30×30×1.5 cm³) and dried. Thegreen body thus produced is freed from the organic constituentspolystyrene place holders, PMMA, residual solvent) by slowly heating toca. 400° C. (0.5 K/min) under hydrogen. The mould is then heated in thesame kiln at 5 K/min from room temperature to 1000° C. Sintering iscompleted in a vacuum kiln (10⁻²-10⁻³ mbar), the pre-sintered specimensbeing brought from room temperature to 1300° C. at 10 K/min andmaintained at this temperature for 2 h. The volume of the fully-sinteredspecimens is ca 0.4 l lower than the initial volume (ca 1 l). This isequivalent to a linear contraction of ca 26%. The pores (as a result ofthe place-holders) have reduced from 1 mm originally to 1.5 mm in thegreen state, equivalent to a reduction of 0.74 to 1.1 mm and a materialdensity of ca 7.4 g/cm³ is achieved in the metallic area.

Example 1.8 Mechanical Properties of a Hot-Pressed Fe22Cr7V0.3Y-Alloy

The PZD powder is produced as described in Example 1, although unlike inExample 1 an atomised Fe22Cr7V0.3Y alloy is used as the educt (insteadof Nimonic® 90 powder).

The processable powder blends summarised in Table 3 were produced in anEirich mixer from the PZD powder produced accordingly and conventionalspherical powders (−25 μm, −53 μm/+25 μm).

TABLE 3 Fe22Cr7V0.3Y powder with varying contents of PZD powdersContents in the relevant blend [wt. %] KON_718 (F) KON_178 (G) PZD_718(−25 μm) (−53 μm + 25 μm) Description [D50: 12 μm] [D50: 13 μm] [D50: 13μm] 18.1 0 100 — 18.2 100 0 — 18.3 50 50 — 18.4 50 — 50

Before processing by hot pressing, partial quantities of 18.2, 18.3 and18.4 are subjected to debinding at a heating rate of 2 K/min from roomtemperature to 600° C. under hydrogen. The hot pressing takes placeunder the following conditions: 1150° C./2 h/35 MPa/argon 4.8 in agraphite mould. After hot pressing, the temperature is reduced by ca 5to 15 K/min, until room temperature is reached. The discs thus producedhave a diameter of ca 100 mm. Tensile test specimens are produced fromthem by water jet cutting as in Example 1 and are ground to the samethickness (ca 3.4 mm). All samples have virtually the same materialdensities of 7.55 to 7.50 g/cm³. The results of the mechanical tensiletest at room temperature are given in Table 4.

Table 4 shows that the strength values Rp0.2 and Rm are better for allPZD powders containing variants (Rp0.2: +5-70%/Rm; +20-50%). 18.1 hasthe best values for elongation (At-Fmax: elastic and plastic part), thePZD-containing variants achieve At-Fmax values of 95 to 45%. In viewalso of the fact that variants 18.2, 18.3 and 18.4 are at allprocessable by pressing and sintering techniques, the basic advantagesof metallic powder blends according to the invention result.

TABLE 4 Results of the mechanical test (Rp0.2, Rm and At-Fmax) forhot-pressed FeCrVY specimens Mechanical properties (at room temperature)Rp0.2 Rm At-Fmax Name [MPa] [MPa] [%] 18.1 405 730 17.5 18.2 700 1100 818.3 430 870 16.5 18.4 480 870 15.5

Example 19 Mechanical Properties of ‘Freely-Sintered’ Fe22Cr7V0.3YPowder Compacts

By mixing the powder blends 18.1, 18.2, 18.3 and 18.4 listed in Table 3with Licowax as a pressing auxiliary agent, the powder mixtures 19.1,19.2, 19.3 and 19.4 are obtained. With these, it is possible to obtain,by monoaxial pressing, moulded bodies in the form of tensile test bars(A (area in direction of pressing): 6.35 cm² l (length in the directionof pressing): 4-5 mm, p: 700 Mpa). The quantity of Licowax is selectedin each case so that the compacts contain a total of 4 wt. % of organicconstituents. This high content is necessary only for the PZD-freevariant (18.1 and 19.1), to make it at all possible to obtain thecompacts with sufficient green strength. To improve comparability, theremaining powders were provided with the same quantities of pressingauxiliary agents.

After production the moulded bodies were subjected to debinding (2 K/minfrom room temperature to 600° C.) under hydrogen. Sintering then takesplace in a cool-wall kiln with a Mo heater (Thermal Technology) at fourdifferent temperatures (1290, 1310, 1340 and 1350° C.) under argon 4.8.Heating is carried out at 10 k/min, and the maximum temperature ismaintained for 2 h. After sintering, the specimens were cooled to roomtemperature at a cooling rate of 10 to 15 K/min.

The results are summarised in the tables below. Although the greatestcare was taken, it was not possible to produce testable specimens of19.1 for 1310 and 1340° C. This is not due to the sintering temperature,but to the defects arising after pressing, which are not immediatelyvisible, but frequently result in destruction after debinding. Suchproblems did not arise with 19.2 to 19.4.

It can be established that (in so far as can be determined) allproperties of the specimens according to the invention (19.2, 19.3 and19.4) were the same as or better than those of the conventional powder19.1. At optimum temperatures, an improvement in Rm of +40-130% (Table5.1), in Rp0.2 of 5-45% (Table 5.2), in At-Fmax of +0-270% (Table 5.3)and in of 0-2% (Table 5.4) was achieved. It should be stated,nevertheless, that the sintering process has so far not been optimised.Once this has been done, an improvement in the properties of 19.2 to19.4 can be expected, as they have considerable advantages in thereproduction of properties as a result of their significantly lowertendency to ‘pressing defects’

TABLE 5.1 ‘Influence of sintering temperature on the strain at break offreely-sintered Fe22Cr7V0.3Y specimens’ Sintering temperature [° C.] (2h, Ar 4.8)) Rm/MPa 1290 1310 1340 1350 19.1 350 240 19.2 525 515 565 55019.3 332 330 360 350 19.4 324 310 170 340

TABLE 5.2 ‘Influence of the sintering temperature on Rp0.2 offreely-sintered Fe22Cr7V0.3Y specimens’ Sintering temperature [° C.] (2h, Ar 4.8)) Rp0.2/MPa 1290 1310 1340 1350 19.1 290 215 19.2 410 380 425335 19.3 290 295 305 300 19.4 280 275 290

TABLE 5.3 ‘Influence of the sintering temperature on the elongation(At-Fmax) of freely-sintered Fe22Cr7V0.3Y specimens’ Sinteringtemperature [° C.] (2 h, Ar 4.8)) At-Fmax/% 1290 1310 1340 1350 19.1 40.15 19.2 7 9 12 15 19.3 2 1 4 4 19.4 2 2 0.8 4

TABLE 5.4 ‘Influence of the sintering temperature on the density offreely-sintered Fe22Cr7V0.3Y specimens’ Density/g/cm³ (theor. density:Sintering temperature [° C.] (2 h, Ar 4.8)) 7.5 g/cm³ 1290 1310 13401350 19.1 6.3 6.6 19.2 6.4 6.5 6.6 6.7 19.3 6.4 6.4 6.3 19.4 6.6 6.7 6.7

Example 20 Sintering Behaviour of Fe20Cl0Al0.3Y Alloys

The PZD powder is produced in the same way as Example 1. Instead ofNimonic® 90 powder, an atomised Fe20Cr10A10.3Y alloy is used as aneduct. The PZD powder produced is called 20.1 (PZD-720) and thereference powder 20.2 (KON-720). Table 6 contains information about thepowder blends processed. Licowax was used as the pressing auxiliaryagent.

TABLE 6 ‘FeCrAlY powder containing 4% pressing auxiliary agent’ Contentof each blend [wt. %] PHM + organic PZD_720 KON_720 Constituents Name[D50: 15 μm] [D50: 14 μm] [wt. %] 20.2 0 100 4 20.1 100 0 4

The powders contained in Table 6 are processed to tensile test bars(A:6.35 cm², 1:4 . . . 5 nm; p:700 MPa). Test specimens were producedfor dilatometer measurements by abrasive cutting (vertically to thedirection of pressing), which were then measured vertically to thedirection of pressing. Measurement comprised, in addition to slowheating at a heating rate of 2 K/min from room temperature to 500° C.for debinding, heating to 1320° C. at 10 K/min (holding time: 10 min)and cooling at a cooling rate of 10 K/min from 1320° C. to roomtemperature. The result is shown in FIG. 7. The heating rate isrepresented by the lower, un-annotated curve, the curve for 20.1 iscontinuous and the curve for 20.2 is interrupted. The results arecollected in Table 7. The path of contraction shows that the powdercompacts of the conventional powder 20.2 undergo elongation up to ca1290° C. as a result of the thermal elongation coefficient. There is nocontraction maximum up to a temperature of 1320° C. To achieve this, thesintering temperature would have to be increased. However, the sinteringshrinkage of the PZD sample 20.1 begins already at ca 1000° C. The firstcontraction maximum, which is not shown, is at ca 1300° C. Thiscorresponds to the behaviour disclosed in patent applicationPCT/EP/2004/00736 of conventional powders produced by atomisation and ofthe PZD powders produced there. It is noteworthy also, that although20.1 has a low starting density of 4.78 g/cm³ (without organicconstituents), a density of ca 7.5 g/cm³ is obtained after sintering. Incontrast to this, the conventional specimen 20.2 achieves only a densityof ca 5.7 g/cm³ at a starting density of 5 g/cm³. The advantages ofsintering PZD powders, apart from the ability to produce powdercompacts, is thus demonstrated.

TABLE 7 Sintering conditions (see notes) Starting density Startingwithout organ, Sintering Sintering density constituents contractiondensity DIL (T, t) [g/cm³] [g/cm³] [%] [g/cm³] 20.2 5.00 4.8 5.84 5.721.1 4.78 4.6 15.17 7.5

1-18. (canceled)
 19. A metallic powder blend comprising a Component I,which comprises a metal, alloy and composite powder having a meanparticle diameter D50 of no more than 75 μm, measured with a Microtrac®X100 particle size analyzer according to ASTM C 1070-01, obtainable by aprocess, wherein the particles of a base powder with a larger or smallermean particle size are processed in a deformation step into flake-likeparticles, whose ratio of particle diameter to particle thickness is110:1 to 10000:1 and these flake-like particles are subjected in afurther process step to pulverization in the presence of a millingauxiliary agent, optionally a Component II, which is a metal powder(MLV) for powder metallurgy applications and optionally a Component II,which is a functional additive.
 20. A metallic powder blend comprising aComponent I, which comprises a metal, alloy and composite powder, ofwhich the contraction, measured with a dilatometer according to DIN51045-1, up to the point at which the temperature of the firstcontraction maximum is reached, is at least 1.05 times the contractionof a metal, alloy or composite powder of the same chemical compositionand the same mean particle diameter D50 produced by atomization, whereinthe powder to be analyzed is compacted before measuring contraction to apressed density of 50% of theoretical density, optionally a ComponentII, which is a metal powder (MLV) for powder metallurgy applications andoptionally a Component III, which is a functional additive.
 21. Themetallic powder blend according to claim 19, wherein Component I or II,independently of each other, are the same or different and have acomposition of Formula (I)hA-iB-jC-kD  (I) wherein, A stands for one or more of the elements Fe,Co or Ni, B stands for one or more of the elements V, Nb, Ta, Cr, Mo, W,Mn, Re, Ti, Si, Ge, Be, Au, Ag, Ru, Rh, Pd, Os, Ir or Pt, C stands forone or more of the elements Mg, Al, Sn, Cu, or Zn, and D stands for oneor more of the elements Zr, Hf, Mg, Ca, or rare earth metal, and h, i, jand k give the proportions by weight, wherein h, i, j and k,independently of each other, each mean 0 to 100 wt. % provided that thetotal of h, i, j and k amounts to 100 wt. %.
 22. The metallic powderblend according to claim 20, wherein Component I or II, independently ofeach other, are the same or different and have a composition of Formula(I)hA-iB-jC-kD  (I) wherein, A stands for one or more of the elements Fe,Co or Ni, B stands for one or more of the elements V, Nb, Ta, Cr, Mo, W,Mn, Re, Ti, Si, Ge, Be, Au, Ag, Ru, Rh, Pd, Os, Ir or Pt, C stands forone or more of the elements Mg, Al, Sn, Cu, or Zn, and D stands for oneor more of the elements Zr, Hf, Mg, Ca, or rare earth metal, and h, i, jand k give the proportions by weight, wherein h, i, j and k,independently of each other, each mean 0 to 100 wt. % provided that thetotal of h, i, j and k amounts to 100 wt. %.
 23. The metallic powderblend according to claim 21, wherein B stands for one or more of theelements V, Cr, Mo, W or Ti, C stands for one or more of the elements Mgor Al and D stands for one or more of the elements Zr, Hf, Y or La. 24.The metallic powder blend according to claim 23, wherein said compositepowder having a mean particle diameter D 50 of no more than 25 μm, hstands for 50 to 80 wt. % i stands for 15 to 40 wt. % j stands for 0 to15 wt. % and k stands for 0 to 5 wt. % provided that the total of h, i,j and k amounts to 100 wt. %.
 25. The metallic powder blend according toclaim 22, wherein B stands for one or more of the elements V, Cr, Mo, Wor Ti, C stands for one or more of the elements Mg or Al and D standsfor one or more of the elements Zr, Hf, Y or La.
 26. The metallic powderblend according to claim 25, wherein h stands for 50 to 80 wt. % istands for 15 to 40 wt. % j stands for 0 to 15 wt. % k stands for 0 to 5wt. % provided that the total of h, i, j and k amounts to 100 wt. %. 27.The metallic powder blend according to claim 20, wherein Component Iand/or II is an alloy selected from the group consisting ofFe20Cr10Al0.3Y, Fe22Cr7V0.3Y, Ni117Mo15Cr6Fe5W1Co, FeCrVY,Ni20Cr16Cu2.5Ti1.5Al, Ni53Cr20Co18Ti2.5Al1.5Fe1.5 and Ni57Mo17Cr16FeWMn.28. The metallic powder blend according to claim 20 which furthercomprises a processing auxiliary agent or a pressing auxiliary agent.29. The metallic powder blend according to claim 19, which is a blend ofComponents I and II.
 30. The metallic powder blend according to claim19, which is a blend of Components I and III.
 31. The metallic powderblend according to claim 19, which is a blend of components I, II andIII.
 32. The metallic powder blend according to claim 20, which is ablend of Components I and II.
 33. The metallic powder blend according toclaim 20, which is a blend of Components I and III.
 34. The metallicpowder blend according to claim 20, which is a blend of components I, IIand III.
 35. The metallic powder blend according to claim 20, whichcontains as Component III a hard material, a slip agent or anintermetallic compound.
 36. The metallic powder blend according to claim20, wherein Component III comprises carbides, borides, nitrides, oxides,silicides, hydrides, diamonds, or sulfides.
 37. The metallic powderblend according to claim 20, wherein Component III comprises carbides ofthe elements of groups 4, 5 and 6 of the periodic system, borides of theelements of groups 4, 5 and 6 of the periodic system, nitrides of theelements of groups 4, 5 and 6 of the periodic system, oxides of theelements of groups 4, 5 and 6 of the periodic system, oxides ofaluminium and rare earth metals; silicides of aluminium, silicides ofboron, silicides of cobalt, silicides of nickel, silicides of iron,silicides of manganese, silicides of molybdenum, silicides of tungsten,silicides of zirconium, hydrides of tantalum, hydrides of niobium,hydrides of titanium, hydrides of magnesium, hydrides of tungsten,graphite, oxides, molybdenum sulfide, zinc sulfide, tin sulfide (SnS,SnS₂), copper sulfide; boron nitride, titanium boride or intermetalliccompounds with particular magnetic or electrical properties on a rareearth-cobalt or rare earth-iron base.
 38. The metallic powder blendaccording to claim 19, wherein Component III comprises long-chainhydrocarbons, waxes, paraffins, plastics, fully-degradable hydrides,refractory metal oxides, organic or inorganic salts or mixtures thereof.39. The metallic powder blend according to claim 20, wherein ComponentIII comprises low-molecular polyethylene or polypropylene,polyurethanes, polyacetal, polyacrylates, polystyrene, rhenium oxide,molybdenum oxide, titanium hydride, magnesium hydride or tantalumhydride.
 40. A process for the production of a molded object, whichcomprises subjecting a metallic powder blend according to claim 20 to apowder-metallurgic molding process.
 41. The process according to claim40, wherein the powder-metallurgic molding process is selected from thegroup consisting of pressing, sintering, slip casting, sheet casting,wet-spraying, powder rolling (both hot, cold or warm powder rolling),hot pressing, and hot isostatic pressing (HIP), sinter-HIP, sintering ofpowder charges, cold isostatic pressing (CIP), green processing, thermalspraying and deposition welding.
 42. A molded object obtainable by aprocess according to claim
 41. 43. A molded object containing themetallic powder blend according to claim 20.